Electric manual machine tool driven by an electric motor

ABSTRACT

A hand power tool that is driven via an electric motor ( 20 ), the electric motor ( 20 ) having a commutator ( 28 ) which is formed of disklike annular segments or laminations ( 32 ), is made more secure against contact spark development by providing that at least one of the laminations ( 32 ) has at least one central recess ( 42, 44, 46 ).

BACKGROUND OF THE INVENTION

The invention is based on a hand power tool.

From European Patent Disclosure EP 350 855, a commutator for a universalmotor is known, of the kind also provided for hand power tools. Itslaminations have the outer contour of a low rectangle whose short sideshave U-shaped openings into which an annular armature that bundles thelaminations together in ringlike fashion can be placed. The laminationsare also shaped in the form of bars and, at the operating speed ofapproximately 3000 rpm of the electric motor that carries thecommutator, they are subjected to relatively strong forces that bend theindividual laminations outward and cause the commutator, on its outsideoriented toward the carbon brushes, not to have a flat, cylindricalcontour but rather to have the tendency of having a curved convexcontour. As a result, the contact area between the arched outside of thecommutator and the flat carbon brushes is reduced considerably,resulting in increased spark development between the carbon brushes andthe commutator; both the commutator and the carbon brushes sufferconsiderable wear or damage from the high temperatures in the arc.

In known commutators of hand power tool motors, the attempt has beenmade to counteract their deformation at high rpm by means of annulararmatures, which keep the annularly bundled laminations that form thecommutator prestressed radially inward. This arrangement has had onlypartial success, and despite the provisions described the knowncommutators are only inadequately secured against deformation and arerelatively complicated and expensive to produce and install.

SUMMARY OF THE INVENTION

The present invention has the advantage that even at extremely high rpmthe commutator does not become perceptibly performed and consequencesassures a low-spark contact with the carbon brushes. As a result, wearof both the carbon brushes and the commutator is slight, and the servicelife of the applicable electrical motor is prolonged. Its efficiency isimproved, since more electrical power is converted into work and lessinto heat. Furthermore, because of the lesser amount of arcing,interference in the radio wave range is less, and interferencesuppression for the hand power tool is simplified or can be dispensedwith.

Because the commutator lamination has at least one central recess, itforms a bar profile that is dimensionally stable and that because of thehigh radial acceleration presents high resistance to deformation orbending in response to deformation forces oriented transversely to thelongitudinal axis and that because of the reduction in mass is exposedto lesser forces of deformation than commutator laminations known beforenow.

Because the recess extends centrally transversely through thelamination, the lamination packet bundled annularly relative to thecommutator forms an annular conduit through which cooling air can bepassed, or which can be engaged by a further annular armature, whichprestresses the laminations radially inward at the center so that athigh rpm they can be deformed radially outward only slightly.

Because the recess is punched, and a thin residual wall remains, thestructure of the material comprising the lamination is strengthened andthe dimensional stability is improved because of the profile formation.

Because the recess is designed as a windowlike opening through which thelamination reaches completely, a mass-reducing annular conduit is formedin the commutator; compared to previous embodiments, this enables abetter distribution of the adhesive or compacting compound for holdingthe commutator together.

Because a recess extends longitudinally through the barlike lamination,the lamination is lighter than a solid lamination and is at leastequally dimensionally stable. Because of the lesser mass of eachlamination, lesser mass forces are operative, so that at high radialacceleration, the deformation of the laminations or of the commutator isless.

Because the central transverse recess is oval or is an ovally contoured,for instance octagonal, polygon, the corresponding lamination forms anespecially dimensionally stable profile.

Because the lamination has additional, open transverse recesses on bothends, the end regions of the laminations can have a tendency to deformradially outward more markedly than solid laminations. This serves tocounteract arching outward of the middle region of the lamination, sothat the lamination remains flat in the region of contact with thecarbon brushes. The end regions have a cross section that increases fromthe outside inward and thus have increasing bending strength, so thattheir radial deformation outward caused by centrifugal force is reduced.Moreover, the compacting compound or the adhesive can become betterdistributed in the region of the voids.

Because the ends of the barlike laminations form a fan blade, anadditional cooling air flow is generated around the commutator orthrough it and, because of better cooling, markedly improves theefficiency of the electric motor equipped with the commutator of theinvention.

Because a cooling air flow is passed through the recess, the individuallaminations and thus the entire commutator can be cooled. This precludesa heat buildup and overheating of the electric motor.

Because a prestressable annular armature reaches through the centraltransverse recess, the deformation of the laminations at high radialacceleration can be counteracted.

Because the transverse recesses form everted features toward one side ofeach lamination, the laminations in the annular composite structure forman especially stable structure that is secure against deformation.

Because the laminations are provided with fan blades on their outer endsacting as contact lugs, the cooling of the motor in the commutatorregion is improved.

DRAWINGS

The invention is described in further detail below in terms of anexemplary embodiment in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1, a longitudinal section through a hand power tool with auniversal motor;

FIG. 2, the three-dimensional longitudinal section through a commutator;

FIG. 3, a cross section through a collector of the invention;

FIG. 4, a further longitudinal section through a collector of theinvention; and

FIG. 5, a single lamination of the commutator.

FIG. 6, a different variant of a single lamination; and

FIG. 7, a further variant of a single of the commutator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a longitudinal section through a hand power tool 10,designed as an eccentric wiper, whose stepped-cylindrical housing 12 hasa vertically extending longitudinal axis 13 from which a main handle 14extends essentially vertically radially outward, and an extra handle 18extends in the opposite direction, that is, toward the front. On theunderside of the main handle 14, there is a button 16 of a switch, notidentified by reference numeral, that is provided for turning the handpower tool drive 10 on and off.

Centrally in the housing 20 or relative to the longitudinal axis 13, anelectric motor 20 is provided, whose stator 22 is embraced without playby the housing 12 and fixed, and whose central rotor 24 comprises acentral rotor shaft 25 that is equipped with radially outward-extendingrotor blades. The rotor blades 26 are penetrated by an electrical wirewinding, not identified by reference numeral, which is electricallyconnected to a commutator 28 in a known manner. The commutator 28 isseated on the upper end of the rotor 24 on the rotor shaft 25, whose endis in turn rotatably supported in a bearing 29 structurally connected tothe housing. The commutator 28 is contacted electrically ondiametrically opposite sides by two carbon brushes 30, which are braced,prestressed radially inward by means of springs 31, on the commutator28.

The commutator 28 is composed of many laminations 32 joined together toform a ring. The laminations are spaced apart from one another by anelectrical insulation 43 that forms a small interstice. Toward thebottom in the viewing direction, the rotor shaft 25 continues in theform of a drive shaft 36, where it drives a fan and a wiper plate 38 torotate.

FIG. 2 shows a variant of a commutator 28 of the invention in the forman enlarged detail. Its structure becomes clear as a result and is basedon a central supporting cylinder 41, which is embraced by a tubularinsulation layer 43, around which an annular packet of elongated, narrowlaminations 32 of V-shaped cross section is composed. Each lamination 32changes into a hook 50 bent outward at a right angle, which serves as acontact lug for connection to the electrical leads, not identified byreference numeral, of the rotor winding. Each of the low, elongatedlaminations 32, adjacent to the next lamination 32, has a radially flatelectrical insulation layer 34. On both ends, each lamination 32 hasgroovelike peripheral recesses 48, through which a prestressable annulararmature 40 reaches that keeps each individual lamination 32 prestressedradially inward against the support tube 41. As a result, at least theends of the commutator laminations 32 are prevented from becomingdetached radially outward from the support cylinder 41 or insulationlayer 43 at operating speed in response to the high radial accelerationat approximately 30000 rpm.

Through a central recess 42 and a trapezoidal design of the outer ends45 of the laminations, each individual lamination 32 is given a shapewhich reinforces its middle and end regions in such a way that they donot arch radially outward perceptibly even at extremely high rpm of therotor. As a result, even at extremely high rpm, the lamination 32remains level or straight on the outside, so that optimal electricalcontact with the straight contact faces of the carbon brushes 30 isassured, and no convex longitudinal arching motions cause linear contactand hence increased spark development.

FIG. 3 shows a cross section through the commutator 28; its laminations32 of V-shaped cross section can be seen as they are made into a packetto form an annular structure, and the vertical insulation layer 34 andthe hooks 50 on the side of the rotor can also be seen. The hooks 50 areprovided with additional, fan-bladelike, punch-indented surfaces forcooling. All laminations 32 are provided with longitudinal recesses 44,46, which extend through the entire lamination and lend itfurther-improved dimensional stability and reduce its mass.

FIG. 4 shows a longitudinal section through a further exemplaryembodiment of a commutator 280, whose support tube 410 is provided withundercut grooves 411 which are engaged by a tubular insulation layer 430so that it is firmly held, and this layer in turn supports an annularpacket of laminations 32, with hooks 50 acting as contact lugs and witha central recess 42. These laminations 32 are potted with the insulationlayer 43 and are firmly held by their entrance into the peripheralrecesses 48.

On their outer ends, the laminations 32 have fan blades 52 for improvingthe motor cooling in the region of the commutator.

FIG. 5 shows the detail of a lamination 32, its V-shaped cross section,and its peripheral recesses 48 and central recess 42, as well aslongitudinal recesses 44, 46. Moreover, the side faces have impressedangular indentations, which further reinforce the structure of thelamination 32 and improve a form-locking connection with the respectiveinsulation layer 34.

FIGS. 5, 6 each show one exemplary embodiment of a lamination withtrapezoidal outer ends in the region 45; the transversely extendingcentral recess 42 forms an approximate hexagon, and located between itand the peripheral recesses 48 are further transversely extending, smalltriangular openings 55. Triangular notches 60 are also made in the lowerlong edge, diametrically opposite webs 66 of material.

FIG. 7 shows a lamination 3200, which substantially matches that of FIG.5, with the distinction of having a hook 50, acting as a contact lug,with a fan blade 52 and on the other outer end a further fan blade 52for improving the cooling in the commutator region.

1. A hand power tool, comprising an electric motor having a commutator,said commutator being composed of a plurality of laminations having acentral recess and forming a perforated section in said commutator, saidrecess being elongated in an axial direction and configured as acontinuous opening, said laminations further having peripheral recesseswhich are arranged next to said central recess and provide a trapezoidalcontour at ends of a periphery, so that said laminations have ananvil-shaped contour, said central elongated recess extendingtransversely through said laminations and forming an annular conduit,wherein said central recess is configured so that a flow of cooling airis passed through said central recesses in said laminations.
 2. A handpower tool as defined in claim 1 wherein said central recess isconfigured as a punched recess with a closed, thin remaining wall.
 3. Ahand power tool as defined in claim 1, wherein said recess passes inaligned fashion through two diametrically opposed flat sides of saidlaminations.
 4. A hand power tool as defined in claim 1 wherein saidcentral recess is oval.
 5. A hand power tool as defined in claim 1wherein regions of each of said laminations above said central recessare configured so that at operating rpm and operating temperature theydeform in such a way that a face to be electrically contacted withcarbon brushes essentially forms a plane.
 6. A hand power tool asdefined in claim 1, wherein outer ends of said laminations areconfigured so that they act as a fan and put a flow of cooling airthrough said laminations into motion.
 7. A hand power tool as defined inclaim 1; and further comprising an annular armature which reachesthrough a recess selected from the group consisting of said centralrecess and said peripheral recess.
 8. A hand power tool as defined inclaim 7, wherein said annular armature is prestressed.
 9. A hand powertool as defined in claim 1; and further comprising a tubular-stub-likeeverted feature each provided on one side of each of said laminations ina region of said central recess and protruding into said central recesson another side on each adjacent one of said laminations; and aninsulating material provided between two adjacent ones of saidlaminations.